instead of 5 (mostly identical) classes.

Also the following bugs were fixed:

* All pickers now use split buttons. (fdo#45671)
* Color palette now indicates the current color. (fdo#73891)
  (Previous changes related to that bug are reverted as part
  of this commit.)
* Selecting a color from a float panel now updates the
  button. (fdo#77683)
* For Font color/background color in Writer, the color
  that is shown on the button, is always the one that's
  actually used. (Can be a different color after hiding
  the toolbar.)
* For Font color/background color in Writer, the button
  now indicates when we're in the format paintbrush mode.
  (Removed in 085e8a07
  for some reason.)

Change-Id: Idb4829552240c52fb0882aca627c8177bbe2f839